The long-term goals of this research are to develop herpes simplex virus (HSV) vaccine strains that induce protective immunity against genital herpes infections and herpes encephalitis infections occurring throughout the world. This research is designed to test possible improvements in existing recombinant strains as vaccines and to determine if an existing vaccine candidate can induce protection in mice against genital HSV-2 isolates from the US and South Africa and HSV-1 isolates from the US and Mexico. In this application our specific aims are to 1) Make genetic modifications of the HSV-2 dl5-29 vaccine strain to improve its efficacy by insertional mutagenesis of the vhs locus in the dl5-29 double deletion mutant, replacing the HSV-2 vhs gene with the HSV-1 vhs gene, testing properties of the recombinant viruses in cell culture, by determining murine CD8+ T cell responses to the viral strains, and by determining the relative levels of protective immunity induced by the viral strains;2) Construct a new form of HSV-2 vaccine by expressing HSV-2 proteins that are targets of human CTLs in an HSV-1 vector that causes minimal cytopathic effect on infected cells, by testing the induction of HSV-specific CD8+ T cells in mice inoculated with these viruses, and by determining if protection is induced against genital infection in mice immunized with these viruses;3) Determine the efficacy of our herpes vaccine candidate in protection in animal models against challenge by clinical HSV-2 isolates by defining the virulence of these HSV-2 isolates in a mouse genital model, by determining the ability of the dl5-29 vaccine strain to induce protection against US and South African isolates, and by determination of the phenotypic properties and genomic sequence of one of the HSV-2 clinical isolates;4) Determine if dl5-29 will protect against HSV-1 clinical isolates in the mouse eye model and to determine the genomic sequence of one of the HSV-1 clinical isolates. An improved genital herpes vaccine candidate may result from this research. One of the priorities of the NIAID Division of AIDS is "to address the role of herpes simplex virus type 2 (HSV-2) as a cofactor in HIV infection." This research proposes to define HSV-2 vaccine candidates that would be efficacious in the US and one of the areas of highest genital herpes and HIV prevalence, sub-Saharan Africa. Thus, this research should be a high priority for AIDS prevention. In addition, NINDS has a mission to "reduce the burden of neurological disease... borne by people all over the world," and a vaccine to prevent HSV-2 or HSV-1 infection or disease would be directed towards this goal.